Method of manufacturing metal oxide crystal and method of fabricating substrate for solar cell

ABSTRACT

Provided are a method of manufacturing a metal oxide and a substrate for a solar cell. The method of manufacturing the metal oxide according to the inventive concept includes mixing a metal precursor material, a basic material, amphiphilic molecules and distilled water to prepare a metal precursor solution, performing a first heat treatment with the metal precursor solution to form a metal oxide, and performing a second heat treatment with the metal oxide to form a pair of metal oxide disks having a single crystalline structure. A pair of zinc oxide disks includes a first disk, and a second disk separated from the first disk in a perpendicular direction to the first disk.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. non-provisional patent application claims priority under 35U.S.C. §119 of Korean Patent Application No. 10-2013-0094908, filed onAug. 9, 2013, the entire contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

The present invention disclosure herein relates to a metal oxide, andmore particularly, to a method of manufacturing metal oxide used in asolar cell.

As fossil energy is exhausted, researches on alternative energy areactively conducted. Particularly, researches on alternative energy usinginexhaustible natural phenomenon such as the sunlight, the wind, etc.are in the limelight.

A solar cell generates electric energy by using light energy emittedfrom the sun. The solar cell may be classified into a solar cellcomposed of an inorganic material such as silicon or a semiconductorcompound, and a dye-sensitized solar cell in which dye is adsorbed onthe surface of nano-crystalline oxide particles. The solar cell receivesattention as an inexhaustible energy source and an environment friendlyenergy source.

SUMMARY OF THE INVENTION

The present disclosure provides a single crystalline metal oxidemanufactured through a low temperature solution process.

The present disclosure also provides a method of manufacturing a singlecrystalline metal oxide for a solar cell on a mass production basis.

The tasks to be solved by the present inventive concept is not limitedto the above-described tasks, however other tasks not mentioned will beprecisely understood from the following description by a person skilledin the art.

Embodiments of the inventive concept provide methods of manufacturing ametal oxide crystal including mixing a metal precursor material, a basicmaterial, amphiphilic molecules and distilled water to prepare a metalprecursor solution, performing a first heat treatment with the metalprecursor solution to form a metal oxide, and performing a second heattreatment with the metal oxide to form a pair of metal oxide diskshaving a single crystalline structure. A pair of zinc oxide disksincludes a first disk, and a second disk separated from the first diskin a perpendicular direction to the first disk.

In some embodiments, the metal precursor solution may include metal ioncomplexes and amphiphilic molecules disposed between the metal ioncomplexes and having a lamella structure.

In other embodiments, the amphiphilic molecules of the lamella structuremay include outer layers and inner layers disposed between the outerlayers, and the metal complex ions may be disposed on the outer layers.

In still other embodiments, the outer layers may exhibit anionic charge,and the metal complex ions may be cations.

In even other embodiments, hydrophilic functional groups of theamphiphilic molecules may form the outer layers, and hydrophobicfunctional groups of the amphiphilic molecules may form the innerlayers.

In yet other embodiments, the metal oxide may include zinc oxide, theforming of the metal oxide may include forming zinc oxide having ahexagonal system, and single crystalline zinc oxide may have thehexagonal system.

In further embodiments, the amphiphilic molecule may be represented byfollowing Formula 1.

Wherein, n is an integer of 5 to 15.

In still further embodiments, the metal precursor solution may includezinc nitrate hexadrate, and the basic material may includehexamethylenetetramine.

In even further embodiments, the second heat treatment may be performedat from about 350° C. to about 500° C.

In other embodiments of the inventive concept, methods of fabricating anelectrode for a solar cell include providing a preparation solutionincluding a zinc precursor, a basic material and distilled water, addingamphiphilic molecules into the preparation solution to prepare a zincprecursor solution, performing heat treatment with the zinc precursorsolution to form zinc oxide having a hexagonal system, sintering thezinc oxide to form a pair of single crystalline zinc oxide disks, andgrowing the pair of single crystalline zinc oxide disks to form a zincoxide crystal film. The pair of single crystalline zinc oxide disksincludes a first disk and a second disk separated from the first disk ina perpendicular direction to the first disk.

In some embodiments, the zinc precursor solution may include zinccomplex cations, and amphiphilic molecules disposed between the zinccomplex cations. The amphiphilic molecules may have a lamella structure.

In other embodiments, the lamella structure may include outer layersincluding hydrophilic functional groups of the amphiphilic molecules,and inner layers disposed between the outer layers and includinghydrophobic functional groups of the amphiphilic molecules.

In still other embodiments, the amphiphilic molecules may includepolyethylene glycol tert-octylphenyl ether.

In even other embodiments, the second disk may have a size and a shapesame as or similar to those of the first disk, and the second disk maybe overlapped with the first disk from a planar view.

In yet other embodiments, the metal precursor solution may include zincnitrate hexadrate, and the basic material may includehexamethylenetetramine.

The metal oxide of the inventive concept may be manufactured by usingamphiphilic molecules. Accordingly, the metal oxide may have a hexagonalsingle crystalline structure. The size and the shape of the metal oxidemay be controlled by controlling the kind, the concentration and/or theamount of the amphiphilic molecules used.

According to the inventive concept, the crystalline metal oxide may bemanufactured as a solution state at a temperature condition lower than avapor deposition method. Therefore, a film including the singlecrystalline metal oxide may be easily produced in a large area. Thesingle crystalline metal oxide film may be used as an electrode of asolar cell. A solar cell including the metal oxide of the inventiveconcept may show high photoconductivity and stability.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the inventive concept, and are incorporated in andconstitute a part of this specification. The drawings illustrateexemplary embodiments of the inventive concept and, together with thedescription, serve to explain principles of the inventive concept. Inthe drawings:

FIGS. 1 to 3 are mimetic diagrams illustrating the manufacturing processof a metal oxide according to an embodiment of the inventive concept;

FIG. 4 is a cross-sectional view illustrating a metal oxide filmaccording to an embodiment of the inventive concept; and

FIG. 5 is a cross-sectional view illustrating a solar cell according toan embodiment of the inventive concept.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Example embodiments of the inventive concept will be described below inmore detail for sufficient understanding of the constitution and theeffect of the inventive concept with reference to the accompanyingdrawings. The inventive concept may, however, be embodied in differentforms and should not be construed as limited to the embodiments setforth herein. Rather, these embodiments are provided so that thisdescription will be thorough and complete, and will fully convey thescope of the present inventive concept to those skilled in the art.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting of thepresent inventive concept. As used herein, the singular forms areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, steps, operations, and/ordevices, but do not preclude the presence or addition of one or moreother features, steps, operations, and/or devices thereof.

It will also be understood that when a layer (or film) is referred to asbeing ‘on’ another layer (or film) or substrate, it can be directly onthe other layer (or film) or substrate, or intervening layers (or films)may also be present.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various regions, layers (or films), etc.these regions and layers should not be limited by these terms. Theseterms are only used to distinguish one region or layer (or film) fromanother region or layer (film). Thus, a first layer discussed belowcould be termed a second layer. Example embodiments embodied anddescribed herein may include complementary example embodiments thereof.Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this inventive concept belongs.

It will be further understood that terms, such as those defined incommonly used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of the relevant artand will not be interpreted in an idealized or overly formal senseunless expressly so defined herein.

Hereinafter, example embodiments will be described in detail withreference to the accompanying drawings.

FIGS. 1 to 3 are mimetic diagrams illustrating the manufacturing processof a metal oxide according to an embodiment of the inventive concept.

Referring to FIG. 1, a metal precursor material and a basic material aredissolved in distilled water to prepare a preparation solution. Forexample, zinc nitrate hexadrate (Zn(NO₃)₂.6H₂O) may be used as theprecursor material, and hexamethylenetetramine (HMTA, C₆H₁₂N₄) may beused as the basic material. In an embodiment, 0.93 g of zinc nitratehexadrate and 0.44 g of HMTA may be added into 250 mL of distilledwater. The basic material may be dissolved in the distilled water andprovide hydroxide ions (OH⁻).

Amphiphilic molecules 200 may be added into the preparation solution anda metal precursor solution may be prepared. The metal precursor solutionmay include metal complex ions 300. The metal precursor solution may bean emulsion state or a suspension state. Each of the amphiphilicmolecules 200 may include a hydrophobic functional group 210 and ahydrophilic functional group 220. The hydrophobic functional group 210may be provided at one end of each amphiphilic molecule 200 as a tailshape. The hydrophilic functional group 220 may be provided at anotherend of each amphiphilic molecule 200 as a head shape. For example,polyethylene glycol tert-octylphenyl ether represented by the followingFormula 1 may be used as the amphiphilic molecule. The hydrophilicfunctional groups 220 of the inventive concept may exhibit anionicproperties. For example, the alcohol functional group of Formula 1 mayexhibit a negative charge because of the unshared electron pair ofoxygen. For example, the alkyl group and the aromatic group in Formula 1may play the role of the hydrophobic functional group 210.

Wherein, n is an integer of 5 to 15, and preferably, may be 10. However,the present invention is not limited thereto.

The amphiphilic molecules 200 may form a lamella structure in the metalprecursor solution and may play the role of a surfactant. The lamellastructure 100 may mean a layer-shape or a plate-shape structure. Thelamella structure 100 may include outer layers 120 and inner layers 110disposed between the outer layers 120. The hydrophilic functional groups220 may form the outer layers 120. The hydrophobic functional groups 210may face to each other and may form the inner layers 110. However, thestructure of the amphiphilic molecules 200 may not be limited to thelamellar structure but may form various micelle structures according toreaction conditions. For example, the micelle structure formed by theamphiphilic molecules 200 may be controlled by controlling the componentratio of the amphiphilic molecules 200 and the metal precursor material.

The metal complex ions 300 may be cations. For example, the metalcomplex ions 300 may be a zinc ammonium ion (Zn(NH₃)₄ ²⁺). The metalcomplex ions 300 may be disposed adjacent to the hydrophilic functionalgroups 220 exhibiting anionic properties. On both sides of the lamellastructure 100, for example, on the outer layers 120, the metal complexions 300 may be disposed. Accordingly, the amphiphilic molecules 200 mayplay the role of a template of the metal complex ions 300. The shapeand/or the size of the template may be controlled by controlling thekind and/or the concentration of the amphiphilic molecules 200.

Referring to FIG. 2, a first heat treatment may be performed with themetal precursor solution, and a metal oxide 301 may be formed. The metaloxide 301 may have a hexagonal system. In this case, the hydroxide ion(OH⁻) provided from the basic material may assist the metal oxide 301 soas to have the hexagonal system. The first heat treatment may beperformed at about 90° C. for about 24 hours. Then, the metal oxide 301may be washed and centrifuged, and residual material may be removed.After that, the metal oxide 301 may be dispersed in a solvent, forexample, ethanol.

Referring to FIG. 3, a second heat treatment may be performed with themetal oxide (301 in FIG. 2), and a single crystalline metal oxide 1000may be formed. The single crystalline metal oxide 1000 may have theshape of a pair of disks. For example, the single crystalline metaloxide 1000 may include a first disk 1100 and a second disk 1200 disposedwith a distance from each other. Each of the first disk 1100 and thesecond disk 1200 may have a hexagonal system. The second disk 1200 mayhave the same or similar shape and size as the first disk 1100. Thesecond disk 1200 may be overlapped with the first disk 1100 from theplanar view. The single crystalline metal oxide 1000 may have thediameter of about 3 μm and the height of about 5 μm. The singlecrystalline metal oxide 1000 may be a single crystal having a (103)face. The second heat treatment may include an annealing process and asintering process. For example, a metal oxide (301 in FIG. 2) may becoated on a substrate (not illustrated). The substrate (not illustrated)may include a transparent conductive oxide, for example, fluorine dopedindium (FTO). The metal oxide (301 in FIG. 2) may be spin coated on thesubstrate (not illustrated) at a 3,000 rpm condition for 30 seconds. Thesubstrate (not illustrated) coated with the metal oxide (301 in FIG. 2)may be secondly heat treated. The second heat treatment may be performedat a higher temperature than the first heat treatment. For example, thesecond heat treatment may be performed at about 350° C. to about 500° C.When the second heat treatment is performed at a temperature lower than350° C., the single crystalline metal oxide 1000 may not be formed. Whenthe heat treatment is performed at a temperature higher than 500° C.,the single crystalline metal oxide 1000 may not have a desired shape ora desired crystalline structure. The amphiphilic molecules (200 in FIG.2) having the lamella structure (100 in FIG. 2) may be removed duringthe second heat treatment process. Accordingly, a gap may be formedbetween the first disk 1100 and the second disk 1200.

When the single crystalline metal oxide 1000 is formed by a vapordeposition method (for example, a metal organic chemical vapordeposition (MOCVD) method or a VLS growing method), the formation of thesingle crystalline metal oxide 1000 in a large size may beinappropriate. According to the inventive concept, the singlecrystalline metal oxide 1000 may be manufactured as a solution state ata temperature condition lower than the vapor deposition method. Thus,the single crystalline metal oxide 1000 may be easily manufactured on amass production basis.

Hereinafter a metal oxide film and a method of manufacturing the sameaccording to an embodiment of the inventive concept will be described.The repeated contents as those explained in the above manufacturingembodiment of the metal oxide will be omitted.

FIG. 4 is a cross-sectional view illustrating a metal oxide filmaccording to an embodiment of the inventive concept.

Referring to FIG. 4, a film F including the single crystalline metaloxides 1000 may be formed. The single crystalline metal oxide 1000 mayinclude zinc oxide and have a hexagonal system. By growing the singlecrystalline metal oxides 1000 manufactured as an embodiment of FIGS. 1to 3, a film may be manufactured. In an embodiment, the film F may bemanufactured by an electrochemical deposition method. In this case, apreparation solution including the single crystalline metal oxides 1000may be coated on a substrate (not illustrated). The preparation solutionmay be the same as or similar to that explained in the embodimentreferring to FIG. 1. The substrate (not illustrated) coated with thepreparation solution including the single crystalline metal oxides 1000may be used as a working electrode. A counter electrode may be aplatinum electrode. In this case, the single crystalline metal oxide1000 may play the role of a seed. The electrochemical deposition of thefilm may be performed by the cyclic pulse condition of 20 s per 1 V and20 s per 0 V. The substrate (not illustrated) may be a substrate of asolar cell. Alternatively, the substrate (not illustrated) may beremoved after forming the film F. In another embodiment, microwaves maybe applied to the preparation solution including the single crystallinemetal oxides 1000. Accordingly, the single crystalline metal oxides 1000in the preparation solution may grow and form a metal oxide film F. Inthis case, the metal oxide film F may be rapidly manufactured. Accordingto the method of the inventive concept, the metal oxide film F may beeasily produced in a large area.

Hereinafter a solar cell including the metal oxide film manufactured bythe inventive concept will be explained. The repeated contents as thatexplained above will be omitted.

FIG. 5 is a cross-sectional view illustrating a solar cell 1 accordingto an embodiment of the inventive concept.

Referring to FIG. 5 along with FIG. 4, a solar cell 1 may include asubstrate 10, a first electrode 20, an electrolyte layer 30 and a secondelectrode 40.

The first substrate 10 may be one selected from various transparentsubstrates including a glass substrate. Alternatively, the firstsubstrate 10 may be an opaque substrate. The first electrode 20 mayinclude a conductive material, for example, a transparent and conductiveoxide. The electrolyte layer 30 may be provided on the first electrode20. The electrolyte layer 30 may have one phase selected from a liquidphase, a solid phase and a gel. According to the phase of theelectrolyte layer 30, the forming order of the electrolyte layer 30 maybe changed. The second electrode 40 may be formed on the electrolytelayer 30. The second electrode 40 may include a conductive material, forexample, a transparent conductive material. One of the first electrode20 and the second electrode 40 may be an anode, and the other may be acathode.

At least one of the first electrode 20 and the second electrode 40 mayinclude the metal oxide film F explained as the embodiment referring toFIG. 4 above. The metal oxide film F may include zinc oxide. In thiscase, the metal oxide may have an energy band gap of about 3.37 eV andan excitation binding energy of about 60 meV. Accordingly, the solarcell 1 may show high photoconductivity. The first electrode 20 and thesecond electrode 40 are stable to ultraviolet light and may not bedamaged by the sunlight when applied in the solar cell 1.

The single crystalline metal oxide according to the inventive conceptmay be manufactured by using amphiphilic molecules. The singlecrystalline metal oxide may have a hexagonal shape. The type,concentration, and amount of the amphiphilic molecules may be adjustedto control the size and the shape of the single crystalline metal oxide.According to the inventive concept, the single crystalline metal oxidemay be manufactured as a solution state at a temperature condition lowerthan the vapor deposition method. Thus, a film including the singlecrystalline metal oxide may be easily produced in a large area. The filmincluding the single crystalline metal oxide may be used as an electrodefor a solar cell. The solar cell including the single crystalline metaloxide may show high photoconductivity and stability.

The above-disclosed subject matter is to be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments, which fall withinthe true spirit and scope of the present invention. Thus, to the maximumextent allowed by law, the scope of the present invention is to bedetermined by the broadest permissible interpretation of the followingclaims and their equivalents, and shall not be restricted or limited bythe foregoing detailed description.

What is claimed is:
 1. A method of manufacturing a metal oxide crystal,the method comprising: mixing a metal precursor material, a basicmaterial, amphiphilic molecules and distilled water to prepare a metalprecursor solution; performing a first heat treatment with the metalprecursor solution to form a metal oxide; and performing a second heattreatment with the metal oxide to form a pair of metal oxide diskshaving a single crystalline structure, a pair of zinc oxide disksincluding a first disk, and a second disk separated from the first diskin a perpendicular direction to the first disk.
 2. The method ofmanufacturing a metal oxide crystal of claim 1, wherein the metalprecursor solution comprises: metal ion complexes; and amphiphilicmolecules disposed between the metal ion complexes and having a lamellastructure.
 3. The method of manufacturing a metal oxide crystal of claim2, wherein the amphiphilic molecules of the lamella structure includeouter layers and inner layers disposed between the outer layers, and themetal complex ions are disposed on the outer layers.
 4. The method ofmanufacturing a metal oxide crystal of claim 2, wherein the outer layersexhibit anionic charge, and the metal complex ions are cations.
 5. Themethod of manufacturing a metal oxide crystal of claim 2, whereinhydrophilic functional groups of the amphiphilic molecules form theouter layers, and hydrophobic functional groups of the amphiphilicmolecules form the inner layers.
 6. The method of manufacturing a metaloxide crystal of claim 1, wherein the metal oxide includes zinc oxide,the forming of the metal oxide includes forming zinc oxide having ahexagonal system, and single crystalline zinc oxide has the hexagonalsystem.
 7. The method of manufacturing a metal oxide crystal of claim 1,wherein the amphiphilic molecule is represented by following Formula 1:

wherein, n is an integer of 5 to
 15. 8. The method of manufacturing ametal oxide crystal of claim 1, wherein the metal precursor solutionincludes zinc nitrate hexadrate, and the basic material includeshexamethylenetetramine.
 9. The method of manufacturing a metal oxidecrystal of claim 1, wherein the second heat treatment is performed atfrom about 350° C. to about 500° C.
 10. A method of fabricating anelectrode for a solar cell, the method comprising: providing apreparation solution including a zinc precursor, a basic material anddistilled water; adding amphiphilic molecules into the preparationsolution to prepare a zinc precursor solution; performing heat treatmentwith the zinc precursor solution to form zinc oxide having a hexagonalsystem; sintering the zinc oxide to form a pair of single crystallinezinc oxide disks; and growing the pair of single crystalline zinc oxidedisks to form a zinc oxide crystal film, the pair of single crystallinezinc oxide disks including a first disk and a second disk separated fromthe first disk in a perpendicular direction to the first disk.
 11. Themethod of fabricating an electrode for a solar cell of claim 10, whereinthe zinc precursor solution comprises: zinc complex cations; andamphiphilic molecules disposed between the zinc complex cations, theamphiphilic molecules having a lamella structure.
 12. The method offabricating an electrode for a solar cell of claim 11, wherein thelamella structure comprises: outer layers including hydrophilicfunctional groups of the amphiphilic molecules; and inner layersdisposed between the outer layers and including hydrophobic functionalgroups of the amphiphilic molecules.
 13. The method of fabricating anelectrode for a solar cell of claim 10, wherein the amphiphilicmolecules include polyethylene glycol tert-octylphenyl ether.
 14. Themethod of fabricating an electrode for a solar cell of claim 10, whereinthe second disk has a size and a shape same as or similar to those ofthe first disk, and the second disk is overlapped with the first diskfrom a planar view.
 15. The method of fabricating an electrode for asolar cell of claim 10, wherein the metal precursor solution includeszinc nitrate hexadrate, and the basic material includeshexamethylenetetramine.